Accelerator magnet structure



` Inventor: VViHem F. \/\/es1:e1"1c1lo1"p,l by FVW/75,() M7 HisAttorney.

w. F. wEsTl-:NDORP- ACCELERATOR MAGNET STRUCTURE Filed Aug. 7, 1946 Figilllllmlllllllli 11 llllllllillll IIIIUIH Dec. 13, 1949 Patented Dec. 13,1.949 f- UNITED ACCELERATOR MAGNET STRUCTURE Willem F. Westendorp,Schenectady, N. Y., assignor to General Electric Company, a corporationof New York Application August 7, 1946, Serial No. 688,902

(Cl. Z50-27) 7 Claims.

The present invention relates to devices in which a stream of chargedparticles is caused by a time-varying magnetic field to be acceleratedin a circular path until they have attained a desired speed. They may bedischarged nally upon a metal target resulting in the production of X-rays. Devices of this kind are described and shown in my prior Patents2,394,071, 2,394,072 and 2,394,073 all of February 5, 1946.

The magnetic eld in such devices as heretofore constructed has beenundesirably non-uni- :termin phase, with the result that part of theinjected electrons were deflected out of their course and caused to beprematurely discharged.

In a magnetic accelerator of former construction the paths of themagnetic lines of ux were of unequal length through the various parts ofthe magnetic structure. The magnetic flux which travelled a short pathin the magnetic core of such accelerator resulted in less hysteresis andeddy current loss than the magnetic ux which traveled a longer path. Thehigher energy loss in the parts of the core remote from the center maybe regarded as caused by electric currents which are in phase with thevoltage and lag 90 degrees with respect to the main magnetizing current.Such currents would produce a non-uniform magnetic iield at the electronorbit. This disturbing magnetic field is strongest at the critical partof the cycle of operation of the accelerator namely at the moment ofinjection of the electrons when the guiding magnetic eld should be weak.It is the object of my invention to produce uniformity of the magneticguiding field at the electron path, particularly at the instant ofelectron injection, which results in high efficiency of operation.

In accordance with my invention, compensating windings are provided forone or more sections oi the core and these windings are eitherresistance loaded or are separately excited or are so inter-connected asto compensate for the inequality of magnetic flux in diierent parts ofthe core no matter what the cause may be.

The accompanying drawing shows in Fig. 1 a iront elevation of anelectron accelerator which is shown in simplified form; Fig. 2 is apartly sectional plan view oi the lower half of an accelerator, shown asprovided with interconnected compensating windings, the section beingtaken at the region indicated by dotted lines in Fig. 1, and

3 and 4 illustrate somewhat diagrammatically other embodiments of myinvention.

An accelerator, as shown in Fig. 1 commonly comprises a magnetic core Ihaving generally circular pole pieces 2, 3 which are coaxial with anannular evacuated accelerating chamber 4. The core I ordinarily consistsof laminations as indicated in Fig. 2. The pole pieces 2, 3 of the coreare tapered near their extremities which may be terminated by flatsurfaces. Two laminated iron discs 5, 6 are supported by insulatingdisks 40 between the pole faces for the purpose of decreasing thereluctance of the magnetic path at this region.

The magnetic core is excited by a pair of seriesconnected windings 1, 3which surround the pole pieces t', 3 and which are energized by analternating current source, (not shown) to provide a time varying cyclicflux in the magnetic circuit traversing the chamber 4.

Within the chamber 4 is provided a thermionic cathode 9 as a source ofelectrons, such cathode is only diagrammatically indicated as the abovenoted prior patents describe its construction. A cooperating anode IBalso is schematically indicated, the anode being connected to aconductive nlm 42 which lines the chamber fi. As the generalconstruction of the magnetic core is described in my prior patentsreference may be had to such patents for more detailed understanding.

As well understood, the time-varying magnetic flux enclosed by theannular chamber 4 causes the electrons emitted by the cathode 9 to becontinuously accelerated as they execute repeated revolutions during aquarter of a cycle of magnetic iiux variation. As a result the electronsmay be caused to assume energies of many millions of electron volts as aconsequence of the continuous acceleration. As described in priorpatents the annular stream of electrons is contracted in diameterautomatically when discharge of the electrons upon the target I0 isdesired.

Distributional variations in eld strength occurring for any reason, forexample, as a result of the transverse difference of flux lengths of theelements of a rectangular core arranged about an annular acceleratingchamber, as heretofore indicated, results in the magnetic flux at thetransverse extremities of the core being out of phase with the ux nearthe center of the core where the core is more closely adjacent to theannular chamber.

As indicated in Fig. 2, I have provided in accordance with oneembodiment of my present invention electric windings II, i2 and I3, Il!which are magnetically interlinked respectively with the extremities ofthe core I as indicated. The windings I I, I2 are connected in serieswith a winding I5 interlinked with a center portion of the core I by theconductors I 6, I'I, I8 and I9. As will be evident from the drawing thewindings II, I2 are connected in opposition to the winding I5. Thewindings I3, I4 are connected by the conductors 20, 2|, 22 and 23 to acenter coil 24 also in opposition. The windings II, I2 and I5 areconnected by the conductors I6, I9 to an adjustable resistor 2B. Theseresistors 25 and 25 are adjusted to load the windings the amountrequired to cause the necessary lag of the flux at the center of thecore.

The loading required to produce the desired lag of the time-varying iiuxat the center of the core may be produced by one or more windings linkedwith the central part of the core as indicated in Fig. 3. Here thewinding 21 is connected to an adjustable resistor 28 which loads thecoil 2'I in order to produce the desired lag. A similar loaded windingmay be provided on the opposite leg of the core as indicated.

As shown in Fig. 4 a coil 2S at one of the extremities of the core I maybe connected to anlexternal source of energy. Here such a source isrepresented by the secondary of 'transformer 3B the voltage of which ishigher than the loop voltage and which is synchronized to be in phasewith the main source of alternating current. The transformer 30, thesecondary winding of which is connected in series with a variableresistor 3l to the winding 29, compensates for phase lag of a portion ofthe iiux by introducing an auxiliary ilux. Other coils ymay be providedas indicated.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. Apparatus for the acceleration oi" charged particles along an orbitalpath comprising a source of alternating voltage; a source or chargedparticles adjacent the locus of said path and energized by said voltagesource to inject said particles into said path; a laminated magneticallyconductive structure including rotationally symmetrical pole piece meansdisposed on either side of said path to provide between them an annulargap containing said path, and core means magnetically coupled to saidpole piece means; annular coil means embracing said pole piece means andenergized by said voltage source to provide a time-varying magneticilux, said flux being directed by said pole piece means and said coremeans to act upon said particles whereby they are inductivelyaccelerated along said and winding means interlinking the laminations ofsaid core means and arranged to compensate for eddy-,current losseiiects produced by said time-varying iiux in said core means.

2. Apparatus for acceleration o1 charged particles along an orbital pathcomprising a source of alternating voltage; a source of chargedparticles adjacent the locus of said path and energized by said voltagesource to inject said particles into said path; a laminated magneticallyconductive structure including rotationally symmetrical pole piece meansdisposed on either side of said path to provide between opposing polefaces an annular gap containing said path, and a substantiallyrectangular core means partially enclosing and in magneticallyconductive relation with said pole piece means; annular coil meansembracing said pole piece means and energized by said voltage source toProvide a time-varying magnetic flux, said flux being directed by saidpole piece means and said co-re means to act upon said particles wherebythey may be inductively accelerated glans said path; and Winding meansinterlinking the laminations of said core means and arranged to reducephase inequalities existing among portions of said time-varying magneticflux directed by said structure.

3. Apparatus for the acceleration of charged particles along an orbitalpath comprising a source of alternating voltage; a source of chargedparticles adjacent the locus of said orbital path and energized by saidvoltage source to inject the particles into said orbital path; alaminated magnetically conductive structure including rotationallysymmetrical pole piece means disposed on either side of said orbitalpath to provide between them an annular gap containing said orbitalpath, and a substantially rectangular core means partially enclosing andin magnetically conductive relation with said pole piece means; annularcoil means embracing said pole piece means and energized by said voltagesource to produce a time-varying flux within said structure whereby saidparticles may be inductively accelerated along said orbital path,portions of said flux following paths of diierent length in saidstructure; and winding means connected in electrical circuit withVresistor means and interlinked with the laminations of said core meanswhereby said time-varying flux may induce currents in said winding meansto reduce phase inequalities existing among the portions of saidtime-varying iiux which follow paths of different lengths in saidstructure.

4. Apparatus for the acceleration or" charged particles along an orbitalpath comprising a source ci alternating voltage; a source of chargedparticles adjacent the locus of said orbital path and energized by saidvoltage source to inject the particles into said orbital path; alaminated magnetically conductive structure including rotationallysymmetrical pole piece means disposed on either side of said orbitalpath to provide between them an annular gap containing said orbitalpath, and a substantially rectangular core means partially enclosing andin magnetically conductive relation with said pole piece means; annularcoil means embracing said pole piece means and energized by said voltagesource to produce a time-varying flux within said structure whereby saidparticles may be inductively accelerated along said orbital path,portions of said iiux following paths of dilerent lengths in saidstructure; and winding means interlinking the laminations of said coremeans and energized by said voltage source to provide an auxiliary fluxwithin said laminations whereby phase inequalities existing among theportions of said time-varying iiux which follow paths of differentlengths in said structure may be reduced.

5. 1n apparatus for the acceleration of charged particles in an orbitalpath by the production of a time-varying flux which links the path toaccelerate the particles and simultaneously establishes a magnetic fieldat the locus of the path to constrain the particles to the path, thecombination which comprises a laminated magnetically conductive coremeans partially surrounding the path to provide a magnetic circuit lorthe timevarying flux and a 'winding interlinking the ,laminations ofsaid core means to produce within said laminations an auxiliary ux whichcounteracts eddy-current iluxes generated in said laminations by thetime-varying flux.

6. In apparatus for the acceleration of charged particles in an orbitalpath by the production oi a time-Varying flux which links the path toaccelerate the particles and simultaneously establishes a magnetic eldat the locus of the path to constrain the particles to the path, thecombination which comprises a laminated magnetically conductive coremeans partially surrounding the path to provide a circuit for thetime-varying flux, and winding means connected in electrical circuitwith resistor means and interlinked with the laminations of said coremeans whereby the time-varying ux may induce currents in said windingmeans to compensate for phase inequalities existing among portions ofthe time-Varying ilux.

7. In apparatus for the acceleration of charged particles in an orbitalpath by the production of a time-varying ilux which links the path toaccelerate the particles and simultaneously establishes a magnetic eldat the locus of the path to constrain the particles to the path, thecombination which comprises a laminated magnetically conductive coremeans partially surrounding the path to provide a circuit for thetime-varying flux, and winding means interlinking the laminations ofsaid core means and energized by an alternating voltage source toprovide an auxiliary flux which counteracts eddy-current luxes generatedin said laminations by the time-varying flux.

WILLEM F. WESTENDORP.

REFERENCES CITED UNITED STATES PATENTS Name Date Kerst Sept. 29, 1942Number

